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1 Basel and Procyclicality: A comparison of the Standardised and IRB Approaches to an Improved Credit Risk Method By C. Goodhart and M.Segoviano 1. Introduction. Our procedure here is to try to reconstruct a typical bank portfolio for a country and then, holding the presumed loan book unchanged over time, (i.e. replacing failed loans with loans of a similar quality), to examine how the loan ratings would have shifted, and hence how the capital adequacy requirements (CAR’s) for the banks would have varied over time; for other similar exercises see Kashyap and Stein (2003 and 2004) and Gordy and Howells (2004). To do this we use Moody’s data on U.S. corporate bonds, included on Moody’s Investors Service, Credit Risk Calculator. We can only do this exercise for those countries for which Moody’s data on credit ratings has a long enough time series. Unfortunately this rules out most large European countries since adequate Moody’s data only go back to 1988 for the U.K., 2001 for Germany; 2002 for France; 2003 for Italy; 2002 for Spain. In practice we also used data provided by the Mexican Financial Regulatory Agency and the Norwegian Central Bank on Corporate Loans for these latter two countries. The Mexican data incorporates statistics between 1995 and 2000 and the Norwegian data incorporates statistics between 1988 and 2001. For an earlier exercise along these same lines, and using the same Mexican data set, see Segoviano and Lowe, (2002). Amongst the problems are how to reconstruct a `typical’ bank portfolio; whether, and how, to deal with the problem of failing loans dropping out of the portfolio; and what account to take of the fact that Basel II is a regime change that may make banks alter their `typical’ behaviour. Very briefly, we reconstructed a typical bank portfolio as follows. We assumed that each portfolio consisted of 1000 loans, each one with equal exposure. From each country’s data sources, we obtained the through time proportion of assets (bonds for the U.S. or corporate loans for Mexico and Norway) that were classified under each of the
Transcript
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Basel and Procyclicality: A comparison of the Standardised and IRB Approaches to an

Improved Credit Risk Method

By C. Goodhart and M.Segoviano

1. Introduction.

Our procedure here is to try to reconstruct a typical bank portfolio for a country and

then, holding the presumed loan book unchanged over time, (i.e. replacing failed

loans with loans of a similar quality), to examine how the loan ratings would have

shifted, and hence how the capital adequacy requirements (CAR’s) for the banks

would have varied over time; for other similar exercises see Kashyap and Stein

(2003 and 2004) and Gordy and Howells (2004). To do this we use Moody’s data on

U.S. corporate bonds, included on Moody’s Investors Service, Credit Risk Calculator.

We can only do this exercise for those countries for which Moody’s data on credit

ratings has a long enough time series. Unfortunately this rules out most large

European countries since adequate Moody’s data only go back to 1988 for the U.K.,

2001 for Germany; 2002 for France; 2003 for Italy; 2002 for Spain. In practice we

also used data provided by the Mexican Financial Regulatory Agency and the

Norwegian Central Bank on Corporate Loans for these latter two countries. The

Mexican data incorporates statistics between 1995 and 2000 and the Norwegian data

incorporates statistics between 1988 and 2001.

For an earlier exercise along these same lines, and using the same Mexican data

set, see Segoviano and Lowe, (2002). Amongst the problems are how to reconstruct

a `typical’ bank portfolio; whether, and how, to deal with the problem of failing loans

dropping out of the portfolio; and what account to take of the fact that Basel II is a

regime change that may make banks alter their `typical’ behaviour. Very briefly, we

reconstructed a typical bank portfolio as follows. We assumed that each portfolio

consisted of 1000 loans, each one with equal exposure. From each country’s data

sources, we obtained the through time proportion of assets (bonds for the U.S. or

corporate loans for Mexico and Norway) that were classified under each of the

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reported ratings for a given country. With this information we constructed the

benchmark portfolio that we used to compute capital requirements at each point in

time.

By assuming that the initial bank loan book remains unchanged throughout, this is

equivalent to assuming that failed loans are replaced by loans of similar initial quality.

This is what Kashyap and Stein (2004) did, and seems natural. Gordy and Howells

(2004) argue, however, that banks will aim for a higher quality portfolio during

recessions, and thus will replace failing loans with credits of higher, than initial,

quality. At the macro level it is hard, in most countries, to see where the supply of

such higher quality loans would come from during recessions; in discussion of this

point at a BIS Conference in May 2004, Michael Gordy noted that in the USA high

quality companies tended to shift their borrowing from capital markets, e.g. the

commercial paper market, to banks during recessions. In any case, since risk

spreads on lower quality loans widen during recessions, any extra benefit to the bank

would be slight. So we feel relatively comfortable about our own assumption.

The results of this exercise for the three countries examined are stark. We compared

the implied capital requirements for our `typical’ bank under three regulatory regimes;

first the standardised approach in Basel II, (which is close to that applied in Basel I);

second, the Foundations IRB approach, (i.e. assuming a constant Loss Given

Default, since we have no good time series in any country for average LGD); and

third, an Improved Credit Risk Method (ICRM). This latter uses a Merton approach to

model credit quality changes and an indirect approach to model correlations amongst

the individual credits in the overall portfolio. The construction of an ICRM is, however,

quite complex. The main addition in this note, beyond our associated work, available

at Goodhart, Hofmann and Segoviano (2004), is that we spell out in more detail here

how we do the exercise of estimating the required capital requirements under an

Improved Credit Risk Method (ICRM).

The outline of the paper is as follows. In section 2, we elaborate on the need to

measure portfolio effects for proper credit risk quantification. In section 3, we develop

the ICRM. In section 4, we present the empirical implementation and results. This

section also describes the data and assumptions made to perform the exercise.

Finally, our conclusions are summarised in section 5.

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2. Why a portfolio Approach? Since the quality of the credit portfolio of a bank can change at any time in the future,

there is a need to make frequent calculations of the expected losses that a bank

could suffer under different risk situations. This analysis of uncertainty is the essence

of risk management. Therefore, measuring the uncertainty or variability of loss and

the related likelihood of the possible levels of unexpected losses in a bank’s portfolio

is fundamental to the effective management of credit risk. Sufficient earnings should

be generated through adequate pricing and provisioning to absorb any expected

loss. However, economic capital should be available to cover unexpected credit

default losses, because the actual level of credit losses suffered in anyone period

could be significantly higher than the expected level. The estimation of the profit and

loss distribution of credit portfolios, from which the unexpected losses can be

identified (e.g. 99.9 Percentile loss level), represents the issue to be addressed in

this document.

Figure 1: Credit Portfolio Profit and Loss Distribution (P&L).

Portfolio Losses

The adoption of the portfolio approach to risk analysis (Markowitz (1959)) has been

amply documented and adopted in numerous finance applications1. Under this

theory, investors seek an optimal risk-return relationship when formulating their

investment portfolio.

1 See Cochrane (2001) for numerous examples on asset pricing.

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The model presented in this paper provides a methodology for assessing portfolio

risk due to changes in loan value caused by changes in obligor (ie. borrower’s) credit

quality. Changes in value are caused not only by possible defaults, but also by

upgrades and downgrades in credit quality; the correlation of credit quality variations

across obligors in the portfolio is also considered. This allows us to calculate the

benefits of diversification in the portfolio. Credit risk modellers have already

developed risk management techniques that seek to take account of this portfolio

diversification effect2. In this paper we present a modification to the “Credit-Metrics”

and KMV methodologies that have been used to simulate unexpected losses from

credit risk in analysed portfolios. For detailed exposition refer to the Credit-Metrics

and KMV technical documents. We refer to our modification to the “Credit-Metrics”

and KMV methodologies as an Improved Credit Risk Model: ICRM3.

3. An Improved Credit Risk Method (ICRM).

As already stated, our model assesses portfolio risk arising from changes in loan

value caused by changes in obligor credit quality. Given the composition of a

particular portfolio, all the possible portfolio values and their probabilities are

recorded in the profit and loss (P&L) distribution of the portfolio. This distribution

records both, increases and decreases in the value of the portfolio caused by the

upgrades and downgrades in the loans’ credit qualities. The modelling of the Profit

and Loss distribution of the portfolio (P&L) can be broken down into the following

steps:

3.1 Modeling the distribution of a single loan.

3.1.1 Credit risk migration and the Merton approach.

3.1.2 Loan valuation.

3.2 Portfolio risk calculation.

3.2.1 Joint probabilities.

3.2.2 Indirect approach to model correlations.

3.2.3 Simulation of quality scenarios for the credit portfolio.

3.2.3 Valuation, P&L distribution and unexpected losses.

2Such approaches may be subject to further improvements, but it is not our intention have to suggest possible improvements to each methodology. 3 The term “Improved” refers to the fact that this model does take account of the benefits of diversification. This is in contrast to the IRB approaches that use a “simplified, single risk factor model” See Secretariat of the Basel Committee on Banking Supervision, (2001).

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3.1 Modelling the distribution of a single loan. 3.1.1 Credit Risk Migration and the Merton Approach.

The Merton approach assumes that a firm’s equity can be viewed as a call option on

the firm’s assets with a strike price equal to the book value of the firm’s debts (Merton

(1974)). The intuition behind this assumption is that, given the limited liability of

equity, equity holders have the right, but not the obligation to payoff debt-holders and

take over the remaining assets of the firm. This approach implies that the credit

quality (rating) of a given debtor is related to the difference between the market value

of its assets and its debt.

Under this approach, the change in the value of the assets of a given company is

related to the change in its rating. So, the distribution of the company’s asset returns

can be used to calculate the distribution of the probability of the firm’s rating change.

For the generalisation of this model, it is necessary to include, in addition to the

default state, different credit quality states. This is because in this model, risk comes

not only from default but also from changes in value due to up(down) grades.

Figure2: The Distribution of Assets’ Returns.

AE CD B

Z e Z d Z c Z b

The likelihood of any credit rating migration in the coming period is conditioned on

the current credit rating of the obligor.

Individual likelihoods of migration are usually represented in matrix form. This table is

called a transition matrix. The transition matrix is the table that summarises the

migration probabilities from one credit quality to any other.

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Table1: Transition Matrix.

A B C D E A 0.865047 0.054462 0.011523 0.002826 0.002439B 0.057558 0.806042 0.106912 0.006859 0.014964C 0.005934 0.052618 0.812763 0.060135 0.065386D 0.001516 0.009098 0.058378 0.708470 0.222538E 0.000000 0.000000 0.000000 0.000001 0.999999

To read this table, the credit rating (today) at time t0 is written on the extreme left column. The possible

ratings to which a given loan can migrate at the risk horizon, t1 are written on the top row. For example,

a loan that at t0 is rated as C has 81.2763% probability of remaining in the same rating at t1. The table

indicates that there is a 6.0135% probability that the loan will migrate to a D rating at t1 and there is a

6.5386% probability that the loan will default (column E) at t1. The transition matrix also indicates that

there is a 5.2618% that the loan will migrate to a B rating and so on.

Having the transition probabilities between different credit qualities, and employing

the Merton Approach, it is possible to derive the (market) value of assets that

represent the cut-off values between different credit qualities, as shown in Figure 1.

These cut-off values fulfil the condition that if the change in the market value of the

asset (r) is sufficiently negative, (i.e. smaller than Ze), then the credit falls into

default; if Ze < r < Zd, the credit is rated D, and so on. Taking into consideration the

empirical transition matrix, the cut-off values are obtained by solving the following

equations (e.g. for a loan initially rated as X):

Prob(E|X) = Prob(r < Ze) = ϕ(Ze) (1)

Prob(D|X) = Prob(Ze <r < Zd) = ϕ(Zd) - ϕ(Ze)

Prob(C|X) = Prob(Zd <r < Zc) = ϕ( Zc) - ϕ(Zd)

Prob(B|X) = Prob(Zc <r < Zb) = ϕ(Zb) - ϕ(Zc)

Prob(A|X) = Prob(Zb <r < Za) = 1 - ϕ(Zb)

Where, R is the implied market value of assets, and ϕ is the Normal Cumulative

Density Function (CDF).

3.1.2 Valuation.

In the previous section, we determined the likelihoods of migration to any of the

possible credit quality states at a given risk horizon. In this section, the values at the

risk horizon for these credit quality states are determined. Values are calculated for

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each migration state. These valuations fall into two categories. First, in the event of

up(down) grades, only the change in the value of the bond due to migration is

considered. To obtain the values at the risk horizon corresponding to rating

up(down)grades, a straightforward present value re-valuation is performed. This

revaluation upon up(down)grade accounts for the decreasing likelihood that the full

amount of the loan will be repaid as the obligor undergoes rating downgrades, and

the increasing likelihood of repayment if the obligor is upgraded. Second, in the event

of default, the change in the value of the loan due to its downgrade (to the default

category) is estimated in the same manner; however, the remaining value of the loan

is multiplied by its loss given default (LGD)4.

Table2: Valuation Table.

A B C D E A 0.000000 -0.012525 -0.062947 -0.220099 -0.997560B 0.012525 0.000000 -0.050422 -0.207575 -0.985035C 0.062947 0.050422 0.000000 -0.157152 -0.934613D 0.220099 0.207575 0.157152 0.000000 -0.777461E 0.997560 0.985035 0.934613 0.777461 0.000000 To read this table, the credit rating (today) at time t0 is written on the extreme left column. The possible

ratings to which a given loan can migrate at the risk horizon, t1, are written on the top row. Changes in

the value of the loan due to migration are in the body of the table. For example, if a loan that at t0 is

rated as C, remains at the same rating at t1, has a zero present value change. If the same loan migrated

to a D rating, its present value would be decreased 15.71%. If the loan were upgraded to a B rating, its

present value would be increased 5.04%, and so on. This re-valuation upon downgrades/upgrades

accounts for the decreasing/increasing likelihood that the full amount of the loan will be repaid as the

obligor undergoes migrations.

As already stated, given a current credit rating of the obligor the likelihood of any

credit rating migration in the coming period is conditioned on the current credit rating

of the obligor.

With the transition probabilities indicated by the transition matrix and the possible

values within each migration state indicated by the valuation table, it is possible to

obtain the value distribution for each exposure on a stand-alone-basis. Beyond this,

portfolio credit risk models5 then extend this framework to the portfolio as a whole, in

order to obtain the distribution of value of the complete portfolio, the so called profit 4 The loss given default is estimated as LGD= 1-(percentage of recovery value). When databases allow it, the recovery rates and consequently, the LGD’s are estimated based on loan characteristics, e.g. credit quality of debtor, geographical area, etc. 5 See CreditMetrics (1997) and CreditRisk+ (1997) technical documents for specific details.

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and loss distribution (P&L) from which we will derive the Value at Risk (VaR) figure

used to define capital requirements.

3.2 Portfolio risk calculation.

In section I, we explained the steps followed to obtain the credit risk for a stand-alone

exposure. Here we extend the methodology to a “portfolio”. For reasons of parsimony

the methodology explained here will refer to a portfolio of just two exposures;

however, the methodology applies to a portfolio of any number of elements. In

general, the necessary steps are the same as in the previous section, but there is

one significant addition. Now it becomes necessary to include the contribution to risk

brought about by the effects of credit quality correlations. So, first, we will discuss the

joint likelihoods of credit quality co-movements. Second, we extend the credit risk

calculation for the stand-alone exposure to the multiple exposure case.

3.2.1 Joint likelihood in credit quality. Understanding joint likelihoods allow us to account properly for portfolio

diversification effects. Correlations determine how often losses occur in multiple

exposures at the same time. The portfolio value volatility (risk) will be lower if

correlations between credit events are lower.

In theory, a correlation matrix of changes of credit quality between creditors can be

computed by developing an explanatory model of the changes in the value of the

assets of the borrowers. This approach presents several practical problems for

implementation, the most important being the handling of very large correlation

matrices. Additionally, it is not possible to obtain the changes in the market value of

assets for each particular borrower, since it would be necessary to have specific

information about the internal financial structure of each borrower. These two

disadvantages make it impossible to implement an ideal correlation matrix; for these

reasons we will adopt an indirect (but more manageable) method to introduce the

portfolio diversification effect.

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3.2.2 Indirect approach to model Correlations. The referred indirect method for introducing the portfolio diversification effect was first

presented in Segoviano (1998). It is based on an assumption made by the

CreditMetrics methodology. This methodology makes an a-priori distinction of the

factors that determine the changes in the value of the assets of the borrowers. This

distinction comes from two basic components: the market component and the

idiosyncratic component. By definition, the idiosyncratic component does not

correlate with anything, since it refers to those factors unique for the debtor. But the

market component can then be further disaggregated into several separate

components that allow the portfolio diversification.

rtotal = WM rmarket + WI rIdiosyncratic (2)

Where:

WM: Percentage of returns explained by the market component6.

rmarket: Market component of returns. WI : Percentage of returns explained by the idiosyncratic component.

Iidiosyncratic: Idiosyncratic component of returns.

Next, the market component of Returns can be defined as:

rMarket=HArGDPGeographicallocation+(1-HA)rGDPSectorComposition (3)

Where:

HA: Percentage of the market component explained by the GDP returns of the

borrowers’ country (geographical location). The determination of HA will be explained

in Section 3.

rGDPGeographicalLocation: Borrower’s country (geographical location) GDP’s return. (1-HA): Percentage of market component explained by the GDP returns’ of the

borrower’ s sectoral activity.

rGDPSectorComposition: Borrower’s sectoral activity GDP’s return.

6 In the CreditMetrics technical document, how these weights can be calculated is explained. After empirical implementations, an acceptable value of WM = 70% is derived. For our exercise, we also assume this value.

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Once all the elements that compose the market component of assets’ returns have

been considered, the next step is to calculate the correlations between the

borrowers’ loans making up a credit portfolio.

Given a pair of borrowers, classified under ratings X and Y, whose sectoral activities

are B and V; located in A and E country groups, and with returns expressed in the

following way:

r w r w H r w H rX IX IX MX A A MX A B= + + −( )1

r w r w H r w H rY IY IY MY E E MY E V= + + −( )1

The problem of estimating the correlations among each couple of borrowers in the

portfolio is summarised in the following way:

BVEMYAMXAEEMYAMXXY HwHwHwHw ρρρ )1()1( −−+= (4)

Where:

pAE: is the correlation between different country groups.

pBV: is the correlation between different sectoral activities.

This equation is computed for each pair of borrowers making up the portfolio. The

results of computing this equation are compiled in a (n x n) square matrix, where n is

the number of loans in the portfolio. This matrix is named the correlation matrix

between borrowers and is unique for each portfolio. This matrix is a key variable for

the simulation of unexpected losses, since it incorporates the necessary elements to

quantify the concentration/diversification of the portfolio.

As explained above, the transition matrix indicates the probabilities of quality

changes that a stand-alone exposure with a given rating might experience.

Additionally, when correlations of quality changes between borrowers are involved,

we can compute the joint likelihood of credit up(down)grades between the loans

making up a portfolio.

Debtors with similar characteristics will tend to migrate jointly to different credit

qualities when hit by economic shocks. Debtors with different characteristics will tend

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to migrate separately to different credit qualities when hit by economic shocks. This

implies that credit portfolios concentrated in credits with similar characteristics will

tend to have higher unexpected losses since they will not be diversifying the possible

economic risks.

With these components, we show in the following section how quality scenarios for

the portfolio are simulated. From these quality scenarios, the loss distribution is built

from which it is possible to obtain an estimate of unexpected losses.

3.2.3 Simulation of Quality Scenarios for the Credit Portfolio.

Combining the transition matrix with the correlation matrix between borrowers, and

under the Merton framework that assumes lognormal asset returns (see equation

(1)), we obtain the joint likelihood of credit quality migration and simulate credit

quality scenarios. The simulated quality changes of the components of the portfolio

allow us to estimate the losses or profits that determine the P&L distribution of the

portfolio.

In order to generate these scenarios, the following process is undertaken:

1. Generation of random uniform numbers.

2. Transformation of such random numbers into normal standard random

numbers.

3. Transformation of the normal standard random numbers into normal-

multivariated random numbers with a correlation matrix defined by the

correlations between creditors.

3.2.4 Valuation, P&L Distribution and Unexpected Losses.

Once the credit portfolio quality scenarios have been simulated, we use the

simulated credit quality scenarios to re-evaluate the portfolio exposures as explained

in section I.2. With the portfolio exposures re-evaluated, we obtain the P&L

distribution for the portfolio.

This is done by computing the losses/gains that come from the difference between

initial and final credit qualities in the loans making up the portfolio. The losses/gains

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obtained from the simulation process are used to build a histogram. This histogram

summarizes the loss distribution of the credit portfolio.

Figure 3: Credit Portfolio Simulated P&L Distribution.

Simulated P&L

-32.28

-30.58

-28.88

-27.18

-25.48

-23.79

-22.09

-20.39

-18.69

-16.99

-15.29

-13.59

-11.89

-10.19 -8.

49-6.

80-5.

10-3.

40-1.

70 0.00

1.70

From this distribution a Value at Risk (VaR) is defined from which we obtain the

amount of unexpected losses from the portfolio. The unexpected losses divided by

the total amount of the portfolio represent the percentage that with a given probability

(defined by the chosen percentile) could be lost in an extreme event. Capital

requirements should be such that they can cover these losses.

4. Empirical Implementation and Results.

Our objective here is to try to reconstruct a typical bank portfolio for a country and

then, holding the presumed loan book unchanged over time, (i.e. replacing failed

loans with loans of a similar quality), to examine how the capital adequacy

requirements (CAR’s) for the banks would have varied over time. We have assumed

that each portfolio consisted of 1000 loans, each one with equal exposure. Below we

explained the assumptions taken for the additional variables that were needed to

perform this exercise. We also indicate the databases from which the necessary

information was taken.

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4.1 Data and Assumptions. Geographical distribution of exposures: From the BIS database on consolidated banking claims for the U.S. and Norway, we

obtained the through time proportion of assets invested in different geographical

areas7. Information for Mexico was obtained from the databases provided by the

Mexican Financial Regulatory Agency (CNBV).

Credit quality distribution of exposures: We obtained the through time proportion of corporate bonds that were classified

under each of the reported ratings for the U.S. from the Moody’s investors service

database. In the case of Mexico and Norway, we obtained the through time

proportion of corporate bonds that were classified under each of the reported ratings

from the databases provided by the Mexican Financial Regulatory Agency and the

Norwegian Central Bank.

Sectoral Activity distribution of exposures: We assumed that the simulated portfolios consisted of loans evenly distributed

across the major sectoral activities that comprise GDP8.

Transition matrices: We use Moody’s data on U.S. corporate bonds, included on Moody’s Investors

Service, Credit Risk Calculator. In the event we also used data provided by the

Mexican Financial Regulatory Agency and the Norwegian Central Bank on Corporate

Loans. The Mexican data incorporates information between 1995 to 2000, and the

Norwegian data incorporates information between 1988 to 2001.

Loss Given Default:

We fixed this at 50% in order to make results comparable to the IRB foundation

approach developed by the Basel Committee.

7 Developing: Africa and the Middle East; Asia and Pacific; developing Europe; Latin America. Developed: EU (non-EMU); EMU; Other Industrial; offshore centres. 8 We included the following sectoral activities: financial, building, mining, information technology, retail, textile, chemical, energy, pharmaceutical, tobacco, food production, beverages, electrical.

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Market component of returns:

In equation (3) we assume that firms’ market component of returns are explained by

both the firms’ sectoral activities and geographical locations. In order to get a proxy

of the percentage of the market component of returns that is explained by

geographical location (1-HA), we run the following OLS regressions:

rMarket = C+B rGDPGeographicalLocation + є (5)

Where:

C: is a drift term

rMarket: was obtained by estimating the returns of the Morgan Stanley Capital International

(MSCI) indexes for major sectoral activities9.

rGDPGeographicalLocation: was obtained by estimating GDP growth rates of the analysed

countries.

In general, in regression analysis, the percentage of the total variation of a

dependent variable that is explained by the assumed explanatory variables is

indicated by the measure of goodness of fit, R2 (explained sum of squares over total

sum of squares). Therefore, we took the R2 that was obtained by running the

regressions specified in equation (5) as proxies for the percentage of market returns

that is explained by the GDP growth rates of the analysed countries, e.g., we take

R2~(1-HA). Consequently, (1- R2) ~HA.

Correlations among different country groups and economic activities:

In equation (4), we make use of AEρ , the correlation between different country

groups and BVρ , the correlation between different sectoral activities. The first were

computed using the spreads of syndicated loans for each country group. We

assumed that such spreads measure the riskiness of the financial system in each

9 These indexes are composed as weighted averages of prices of the major corporates in developed economies for specific sectorial activities. The sectorial activities that we considered were: financial, building, mining, information technology, retail, textile, chemical, energy, pharmaceutical, tobacco, food production, beverages, electrical. Source: Datastream.

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− 15 −

country group. The latter were computed from indices of the major sectorial activities

examined in the exercise10.

We used the variables and assumptions described in this section to perform the

simulation of credit quality scenarios with which we re-evaluated the exposures in the

portfolio and computed the P&L of the portfolio.

Simulation:

In this application, we programmed an algorithm to compute 10,000 possible quality

scenarios for each of the (n x n) couples of the loans that make up the portfolio. Each

quality scenario shows a change in the market value of the borrowers’ assets whose

loans compose the portfolio. Since it was assumed that the process that generates

changes in the assets’ log-returns follow a normal distribution, we use a normal-

multivariated distribution to generate joint quality migrations.

10 Idem footnote 9.

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4.2 Results. The results of this exercise for the three countries examined are stark. We have

simulated the time paths of CARs under each of our three approaches, standardised,

IRB Foundation (IRB F) and ICRM, for our various countries, and the results are set

out in Tables 3 to 5, and Charts 1 to 3.

Table 3: CARs for the USA

PERIOD Standardised IRB F ICRM 1982 9.597967 8.591044 8.070189 1983 8.933900 7.185306 6.802057 1984 8.933900 7.624870 7.032411 1985 9.133900 8.024912 7.262765 1986 9.463390 9.989917 8.736384 1987 9.463930 9.824500 8.545390 1988 9.463930 8.659141 6.990717 1989 9.563390 10.804149 6.488127 1990 9.563390 11.677029 7.601025 1991 9.986339 11.434979 7.541649 1992 9.687739 8.064210 6.470195 1993 9.287739 6.468979 4.665018 1994 8.901877 5.395182 3.783256 1995 8.507394 5.561594 4.087216 1996 8.246774 5.646111 4.316443 1997 8.294313 5.940010 4.837646 1998 8.312774 6.508256 5.831926 1999 8.403155 7.810893 6.704727 2000 8.410316 8.126805 7.163834 2001 8.531238 8.245881 7.242604 2002 8.312375 8.180511 6.779526 2003 8.107739 6.603000 6.258685

Average 8.959430 8.016694 6.509627 Variance 0.339964 3.392352 1.945790 Chart 1: CARs for the USA

0.002.004.006.008.00

10.0012.0014.00

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

Perc

enta

ge

Standardised IRB F ICRM

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− 17 −

Table 4: CARs for Norway PERIOD Standardised IRB F ICRM

1989 9.991635 8.311481 7.5801151990 10.265155 9.275921 8.1275731991 10.465155 9.781705 8.6750311992 10.367155 9.929912 9.0343731993 10.265155 9.523779 9.1863051994 10.940239 13.235447 9.8215421995 11.320031 14.06617011.0824871996 10.669155 12.141937 9.7225931997 10.265155 8.857323 7.3173531998 10.265155 9.001267 7.4226211999 10.265155 9.218641 7.5278892000 10.265430 9.486551 7.9305052001 10.360916 9.648655 8.3331222002 10.461360 9.764866 8.343509

Average 10.440489 10.160261 8.578930Variance 0.113401 2.941614 1.190491 Chart 2: CARs for Norway

0.002.004.006.008.00

10.0012.0014.0016.00

1989

1991

1993

1995

1997

1999

2001

Perc

enta

ge

Standardised IRB F ICRM

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− 18 −

Table 5: CARs for Mexico PERIOD Standardised IRB F ICRM Mar-95 8.765096 13.86423010.462123Jun-95 9.221855 16.65079012.285877Sep-95 9.299730 17.10300912.714591Dec-95 9.493498 18.15147012.820000Mar-96 9.251044 17.06754212.589874Jun-96 9.494958 18.44856113.248221Sep-96 9.557249 19.41584314.891864Dec-96 10.303734 24.23094217.645355Mar-97 9.430354 19.08871415.153354Jun-97 9.273425 17.50091113.895955Sep-97 9.396601 18.25420114.344051Dec-97 8.928781 15.19411614.796451Mar-98 8.813186 14.39793213.673818Jun-98 8.851211 14.42816012.256023Sep-98 9.058278 15.54539411.622476Dec-98 9.040916 15.45623411.797630Mar-99 9.052107 15.51928212.003802Jun-99 8.981783 15.29660812.251375Sep-99 9.135013 15.97926512.725803Dec-99 8.968905 15.34540912.100842

Average 9.215886 16.84693113.163974Variance 0.122662 5.644965 2.588205

Chart 3: CARs for Mexico

0.005.00

10.0015.0020.0025.0030.00

Mar

-95

Sep-

95

Mar

-96

Sep-

96

Mar

-97

Sep-

97

Mar

-98

Sep-

98

Mar

-99

Sep-

99

Perc

enta

ge

Standardised IRB F ICRM

The important result to observe is the much greater variance of the simulated

outcomes for the IRB than for the standardised or ICRM approaches. During periods

of strong growth, high profits and low NPLs, (USA in the mid 1990s and Norway in

1997), the IRB has a lower CAR than the standardised approach in all our developed

countries; whereas in recessions, (e.g. USA in 1990/91, Mexico mid 1995/96 and

Norway in 1994/1995), the CAR is markedly higher for the IRB than in the other two

approaches. In Mexico, an emerging market economy (EME), the average quality of

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− 19 −

loan is lower throughout than in developed countries, so the IRB gives a higher CAR

in all years, but, as in developed countries, the variance of the CAR (up in recessions

as in 1995/96, and lower during the better years) is greater for the IRB than in the

other two approaches.

It follows that the % change in the required CAR under the IRB as a country moves

from boom to recession (up) and back to boom again (down) will be much more

extreme under the IRB than under the other two approaches. This is shown in Table

6.

Table 6: Maximum % Change in CARs

A. IRB Upwards Downwards

1 Period Date 2 Consecutive

Periods Dates 1 Period Date 2 Consecutive

Periods Dates

USA 0.25 1989 0.33 1989/90 -0.29 1992 -0.49 1992/93NORWAY 0.39 1994 0.45 1994/95 -0.27 1997 -0.41 1996/97

MEXICO 0.25 Dec 96 0.30 Sep/Dec

96 -0.21 Mar 97 -0.30 Mar/Jun

97 B. ICRM Upwards Downwards

1 Period Date 2 Consecutive

Periods Dates 1 Period Date 2 Consecutive

Periods Dates

USA 0.21 1998 0.33 1998/99 -0.28 1993 -0.47 1993/94

NORWAY 0.13 1995 0.20 1994/95 -0.25 1997 -0.37 1996/98

MEXICO 0.18 Dec-96 0.30 Sep/Dec

96 -0.14 Mar-97 -0.22 Mar/Jun 97

C. Stand Upwards Downwards

1

Period Date 2 Consecutive

Periods Dates 1 Period Date 2 Consecutive

Periods Dates

USA 0.04 Jun-05 0.06 1985/86 -0.07 1983 -0.09 1994/95

NORWAY 0.07 Jun-05 0.10 1994/95 -0.06 1997 -0.10 1996/97

MEXICO 0.08 Dec-96 0.08 Sep/Dec

96 -0.08 Mar-97 -0.10 Mar/Jun 97

5. Conclusions.

The implication of the results of this excercise is that procyclicality may well still be a

serious problem with Basel II, even after the smoothing of the risk curves that were

introduced between Consultative Papers 2 and 3 produced by the Basel Committee

to mitigate this problem. However there will be other potentially offsetting factors.

Banks normally keep buffers above the required minimum CARs, both for their

protection against sanctions should the minimum be infringed and to satisfy ratings

agencies, and these buffers are likely to be raised during booms when IRB CARs

may fall to extremely low levels. Note, however, that we have used Moody’s data for

the U.S.A. from1982 to 2003, for Norway from 1988 to 2001 and for Mexico from

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− 20 −

1995 to 2000, which are already supposed to be averaged over the cycle, whereas

most commercial banks are, so we are told by several of them, likely to use point-in-

time ratings, which could worsen pro-cyclicality yet further.

Basel II will be a regime change, and one of the purposes of this is to make bankers

more conscious of risk assessment and risk management. It has already succeeded

in this. One hope is that it will induce bankers to be more prudent during booms

despite declines in CARs. An implication of a move from the standardised to an IRB

approach is that the individual bank making this transition will be encouraged to shift

its portfolio to higher-quality, higher rated credits, because it then benefits from a

lower CAR. This is good of itself, but the higher the quality the credit, the steeper is

the risk curve, (relating quality to required risk ratio); so the procyclicality is likely to

be enhanced, even if average quality improves.

When a regime change is introduced, no one in truth can predict its ramifications,

certainly not us. Nevertheless these simulations suggest that procyclicality could

remain a serious concern. It is even possible that with the advent of a serious

downturn, if one was to occur, the impact of abiding by the IRB would be too severe

for the authorities in some countries to countenance. Perhaps like the Stability and

Growth Pact it would only be observed in the breach when it began to bite hard.

Possibly an even greater worry might be that the adoption of Basel II, while not being

so adverse as to force reconsideration, might yet exacerbate future capital

fluctuations.

Certainly there remains a tension between relating CARs more closely to underlying

risks in individual banks, and in trying for macro-economic purposes to encourage

contra-cyclical variations in bank lending in aggregate. How to square this circle

must, however, be a subject for future research.

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− 21 −

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